1. Field of the Invention
The present invention relates to oil soluble polyethers.
2. Background Information
Since aliphatic polyethers are in general hydrophilic substances, common polyethers have poor miscibility with hydrophobic substances. This is especially true for the vast majority of polyoxyalkylene glycols which are used as lubricants. Thus, in Ullmanns Encyclopadie der technischen Chemie (Ullmann's Encyclopedia of Industrial Chemistry), Verlag Chemie, Weinheim, 4th edition, volume 20, page 504, Table 29, for example, polyoxyalkylene glycols are classified as being poorly miscible with mineral oils.
Therefore, attempts have been made to develop special polyethers having good miscibility with mineral oils. These polyethers are known as oil soluble polyethers. Oil soluble polyethers are generally modified polymers of propylene oxide. They are derived from the copolymerization of propylene oxide and an alpha-olefin epoxide onto a hydrocarbon starter containing one or more active protons. Oil soluble polyethers are often used as base stocks and components for fully and partially synthetic lubricants. Polyether based lubricants offer longer service life, higher efficiency in gears, bearings, hydraulics, automotive crankcases, etc. and better thermal stability compared to mineral oils. Hence, as indicated in Crachnell, R. B., "Oil Soluble Polyethers in Automotive Crankcase Lubricants", Society of Tribologists and Lubricant Engineers, STLE Preprint No. 92-AM-6E-5, oil soluble polyethers have excellent potential as synthetic lubricant base fluids.
It is known that the various possible polyether types which can be used as base fluids for industrial lubricants present a challenge for the study of their properties. S. Kussi, "Polyethers as Base Fluids to Formulate High Performance Lubricants", Lubrication Engineering, Volume 47, 11, 926-933, November, 1991. Kussi's article discusses the chemical, physical, and tribological properties of different polyether types through specific applications, like metalworking processes and lubrication of gears and bearings. Kussi's article also considers a number of important polyether structures by using different lubricity test equipment.
Although, as Kussi's article indicates, this is a challenging area of research, development of certain polyethers having improved miscibility with mineral oils has occurred. It is known from Japanese Kokai 50/133205 that polyethers having the general formulae R.sup.1 O(AO).sub.n R.sup.2 and R.sup.1 O((AO).sub.m CH.sub.2)(AO).sub.m R.sup.1 where R.sup.1 and R.sup.2 are C.sub.1 to C.sub.24 hydrocarbyl and/or hydrogen, m is 1 to 100, n is 1 to 50 and A is C.sub.p H.sub.2p where p is 2 to 26, can be used as lubricating oils when mixed with mineral oils. Thus, 50/133205 describes polyethers based on ethylene oxide, propylene oxide and/or butylene oxide and a longer-chain 1,2-epoxyalkane with up to 26 carbon atoms having, if desired, one or two hydroxyl terminal groups. The publication discloses that, to guarantee miscibility with mineral oils, the 1,2-epoxyalkane having up to 26 carbon atoms must be present in the polyethers in an amount of approximately 40% by weight or more. In these formulations it is preferred that the mineral oil is the major component. However, such materials tend to have excessive coefficients of shearing friction which makes them unsuitable for many applications. Moreover, in contrast to ethylene oxide and propylene oxide, long-chain 1,2-epoxyalkanes are not petrochemical primary products, and must be prepared synthetically. The incorporation of large amounts of long-chain 1,2-epoxy-alkanes into polyether which are miscible with mineral oils is therefore technically and economically demanding and unsatisfactory.
Mineral oil-soluble polyethers are also described in European Published Specification ("EP-OS") 0,064,236. These are tetrahydrofuran-containing copolyethers which are only accessible by a cationic polymerization process. Such cationic polymerization processes require special reactor materials and equipment due to the aggressive nature of the catalysts. Therefore, they can not be carried out in plants which are customarily used for anionic epoxide polymerizations. In addition, to achieve good miscibilities with mineral oils, long-chain 1,2-epoxyalkanes in amounts of over 40% by weight are in practice necessary even for the polyethers described in EP-OS 0,064,236 (see Comparative Examples V-VIII and Table 2 in U.S. Pat. No. 4,973,414).
If an attempt is made to prepare low-viscous lubricants based exclusively on the polyethers known from EP-OS 0,064,236, for example, those of the important viscosity class ISO-VG 68, it is found that high evaporation losses occur (See Comparative Example 9 in U.S. Pat. No. 4,973,414) which can be repressed for only a short time by means of customary amounts of antioxidants. The addition of large amounts of antioxidants is not a solution to the problem, since it results in a deterioration of the lubricant properties.
Previously, there have been no mineral or synthetic oil miscible polyethers which are technically and economically completely satisfactory in the field of lubricants. Moreover, the prior art described above generally teaches the desirability of using mineral oil/polyether lubricants only when the mineral oil constitutes the major component of the lubricant.
The instant invention provides novel oil soluble polyether compositions that can be used as base stocks and components for fully and partially synthetic lubricants. That is, the novel oil soluble polyethers can be used either in the absence of mineral oil or in mineral oil/polyether mixtures where the mineral oil comprises only the minor component. These novel oil soluble polyether compositions can be used to improve the miscibility of certain oil insoluble polyethers in mineral oil or synthetic oil (e.g., such as hydrogenated polyalpha olefin products). This invention allows for control over viscosity and viscosity index over a broad range. Moreover, this invention allows for the selective control over miscibility in synthetic and mineral oil based lubricants. These oil soluble polyethers are useful as automotive or industrial lubricants and are compatible with conventional mineral oils. Thus, the instant oil soluble polyethers are technically and economically superior to prior art products in the field of lubricants.
Moreover, the oil soluble polyethers of the instant invention have the economic advantage that they are primarily petrochemical primary products and require minimal synthesis as compared to prior art oil soluble polyethers.